Torsional dampers are widely used in association with machine components, for example in the automotive, aerospace and construction industries. Many torsional dampers utilize a viscous damping fluid in conjunction with a relatively heavy rotatable “inertia” ring to damp a broad range of vibration frequencies of a rotating shaft. The fluid is typically sealed within a housing and transfers energy between the inertia ring and the rotating shaft to attenuate torsional vibrations. Utilizing a damper with sufficient fluid viscosity can be a critical factor in successful vibration damping. Over the course of many hours of service, high temperatures and shear forces can chemically and/or physically change the damping fluid such that viscosity is degraded. Consequently, performance of the damper suffers, potentially resulting in undue wear and tear on an associated rotating component, such as a crankshaft in an internal combustion engine.
It has become common in certain industries to scrap used dampers when a machine system, e.g. an engine, is disassembled for remanufacturing. Engineers have recognized for some time that viscous-fluid torsional dampers scrapped upon remanufacturing of the associated engine might still be serviceable. Challenges in separating acceptable dampers from those which are no longer serviceable, however, have inhibited widespread re-use of these components.
Several strategies exist for testing damper performance. On the one hand, dampers may be tested to determine performance by mounting the damper in a test rig and subjecting it to torsional vibrations. The relative effectiveness of the damper at attenuating the torsional vibrations can then be evaluated. While this approach may be worthwhile in some cases, it is quite labor intensive to mount torsional dampers within a test rig, then rotate the torsional damper and measure its damping abilities. Suitable damper testing rigs also tend to be expensive.
Viscosity of the damping fluid can also be tested directly. “Destructive” testing techniques have been used wherein a hole is drilled in a damper housing, and the viscosity of the fluid measured with a viscometer, or by some other means. This approach is also relatively labor intensive, and requires sophisticated resealing techniques for the damper housing, and care to avoid the introduction of contaminants into the fluid. None of the known strategies potentially available to evaluate torsional dampers for re-use has proven both satisfactory and cost effective, particularly for high volume remanufacturing and salvaging.